Abstract Metastatic melanoma remains incurable for the majority of patients. Of the ~39,000 patients diagnosed with Stage IIB-IV melanoma annually, ~50% do not respond to existing treatments and for those that do, resistance is a major concern. Furthermore, survival rates for patients with stage (IIA-IIIB) primary tumors steadily decrease with increasing stage. Prevention of metastasis itself would offer the best chance at cure. Currently, there is no adjuvant therapy that is effective in preventing metastatic spread. To address this need, Rgenix is developing RGX-104 as a first-in-class orally available therapeutic for the treatment of metastatic melanoma. RGX-104 is a Liver X receptor (LXR) agonist, which activates expression of Apolipoprotein E (ApoE), a recently identified tumor suppressor gene. ApoE activates the anti-tumor immunity by suppressing myeloid derived suppressor cells (MDSCs), inhibits cancer cell invasion and angiogenesis. This intricate mechanism, which is fundamentally different from that of existing treatments, results in robust tumor growth suppression and inhibition of metastatic growth in mouse models of melanoma. Strong activity was also observed using cell lines that are resistant to approved therapies (vemurafenib and decarbazine). Furthermore, combining RGX- 104 with approved therapeutics (vemurafenib, anti-CTLA-4 or anti-PD-1) results in additive tumor suppressive efficacy. In depth ADME, pharmacodynamic and pharmacokinetic studies have demonstrated RGX-104 to be an excellent drug candidate. Rgenix has also identified ApoE as a molecular biomarker, which can be measured in the blood as a read-out of response, in mice and monkeys. Here, Rgenix aims to complete pre- clinical development of RGX-104 by developing analytical methods for ApoE PD biomarker measurements of clinical samples, completing GMP scale up synthesis for Phase I clinical trial, and performing safety pharmacology studies. The long-term goal is to develop a safe and efficient therapy for both treating metastatic melanoma and preventing metastasis formation. To this end, Rgenix will perform bioanalytical method development for ApoE measurement in white blood cells by quantitative real-time PCR and for ApoE protein and MDSC content in patient biopsies by immunohistochemistry, using a training cohort of commercially available blood and tumor samples. Success in this in vitro system will set the stage for testing correlation of ApoE expression with treatment outcome during Phase I. This will establish ApoE expression as a surrogate endpoint during clinical development. In addition, routes for GMP scale up synthesis will be refined and a 10- 12kg batch of RGX-104 for human clinical trials produced. Finally, to test potentially harmful effects of the drug during chronic dosing, safety pharmacology studies for cardiovascular function, central nervous system effects and respiratory function will be conducted. Successful completion of these studies will move RGX-104 into the clinic and allow development in both the metastatic and adjuvant settings. Additionally, an easily measurable molecular biomarker reflecting target engagement would accelerate clinical development of RGX-104.